1. Field of the Invention
The present invention relates to a compass with adjusting means for adjusting the compass legs and for changing the distance between the compass points, wherein each compass leg includes a pivot bearing and an adjustment bearing.
2. Description of the Related Art
Compasses of the above-described type are usually composed of two compass legs which are mounted in a compass head and whose points can be adjusted at certain distances relative to each other. The compass leg adjustment is effected manually and also frequently with the aid of adjusting means, particularly adjusting spindles which interact with one or more spindle nuts and which, depending on the pitch of the thread, the unlocking mechanisms or other structural means, facilitate a quick or slow adjustment or change of the distance between the points. The adjusting spindle is usually arranged axially between the compass head and the compass points at a more or less great distance from the compass head and the compass leg ends or the pivot bearings thereof, and the adjusting spindle is mounted so as to be rotatable.
A compass of the above-described type is disclosed, for example, in German utility model 18 32 209. The compass has a rack and an adjusting wheel and is provided with two bearing axes in the compass head in which the compass legs are rotatably mounted. The distance between the points can be adjusted by a turning knob acting on a rack. The fine adjustment is effected by rotating the turning knob, while the coarse adjustment is effected by an increased pressure on the points of the compass legs, wherein the rack and a pinion arranged on the turning knob mesh with each other.
German patent 1 761 101 discloses another compass which includes a rotatable adjusting spindle and an adjusting wheel arranged concentrically on the adjusting spindle. In order to facilitate a quick coarse adjustment, the adjustment spindle has a thread with a coarse pitch and is free of self-locking action. When an increased transverse pressure or tensile force is applied on the points of the compass legs, the adjusting spindle rotates automatically and causes the coarse adjustment, while the fine adjustment is to be effected by manually operating the adjusting screw.
German patent 38 36 683 discloses a similar compass in which the spindle nuts can be resiliently spread apart and can be removed from the spindle provided with a normal thread, so that a so-called quick adjustment is possible when the spindle is unlocked. The fine adjustment of the distance between the points of the compass takes place also in this case by rotating the drive wheel with the aid of the threaded spindle having a relatively fine thread.
The compasses known in the art have the disadvantage that either complicated devices or special spindles are required for a simple and particularly a quick adjustment of the compass legs. On the other hand, an adjustment of the legs with normal adjusting spindles, i.e., spindles having a fine pitch, is only possible in a relatively time consuming and difficult manner.
Another disadvantage of the known compasses is to be seen in the fact that during use, i.e., when drawing circles, it is necessary while continuously changing the center of gravity to make sure that a good contact exists between a point of the compass with a support surface, on the one hand, and of the writing tip with the recording carrier, on the other hand. This becomes more and more difficult as the drawing radius increases.
In addition, it is frequently considered to be disadvantageous that the adjustment of the distances by which the needle and the lead or writing tip protrude beyond the points of the legs influences to a significant extend the circle to be drawn. This makes it impossible to effect an acceptable scaling of the adjustment values by means of a measuring scale or other indicating means.